1. Technical Field
This invention relates in general to integrated circuit (IC) dice and, in particular, to devices and methods for testing dice in IC modules.
2. State of the Art
Integrated circuit (IC) dice are typically tested before they are packaged to determine if they have any failing circuitry. In general, one of the first steps in testing a die is to initiate a test mode in the die by applying control signals to selected bond pads on the die referred to as test bond pads. As an example, most Dynamic Random Access Memory (DRAM) dice manufactured by the Assignee of this invention, Micron Technology, Inc. of Boise, Id., are tested in a test mode initiated, in part, by applying a logic xe2x80x9c0xe2x80x9d signal to their Output Enable (OE) bond pad.
As shown in FIG. 1, when multiple dice 10 are packaged together in an IC module 12, their test bond pads 14 (e.g., their OE bond pads) are often interconnected with their reference voltage bond pads 16 to the reference voltage VSS through module terminals 18 to ensure that a test mode cannot be accidentally initiated in an end user""s system. While this works well to prevent accidental initiation of a test mode in dice in an IC module in the field, unfortunately it also prevents intentional testing of the dice by an IC manufacturer after they are packaged in the IC module.
One conventional solution to this problem, described in U.S. Pat. Nos. 5,278,839 and 4,519,078, is to eliminate the need to initiate a test mode in the manner described above by incorporating self test circuitry into dice. Because the self test circuitry is controlled through address and control bond pads that generally are not fixed to the reference voltage VSS or supply voltage VCC, a test mode can be initiated with the self test circuitry after the dice are packaged in an IC module. However, self test circuitry is a cumbersome and expensive solution that does not address the need for a solution that is easily incorporated into existing dice and IC modules.
Because it would be advantageous to have the flexibility to test dice after they are packaged in an IC module, there is a need in the art for an improved device and method for initiating and performing such testing.
An inventive integrated circuit (IC) module, such as a Multi-Chip Module (MCM), includes a terminal receiving a test mode initiate signal, such as a supply voltage VCC, and an IC die having a bond pad and a function circuit. A switching apparatus, such as a fuse, is connected with the bond pad between the terminal and the function circuit to conduct the test mode initiate signal to the function circuit, and an impedance apparatus, such as a resistor, connected between the function circuit and an operational mode signal, such as a reference voltage VSS, supports a difference in voltages between the test mode initiate signal at the function circuit and the operation mode signal. The function circuit responds to the test mode initiate signal by initiating a test mode in the die. The switching circuit also selectively isolates the function circuit from the die, and the impedance apparatus then conducts the operational mode signal to the function circuit. The function circuit responds to the operational mode signal by entering an operational mode. Thus, a test mode can be initiated in the die after it is packaged in the IC module by providing the test mode initiate signal at the terminal, and the test mode can then be disabled and the die fixed in the operational mode by selectively isolating the function circuit from the terminal with the switching apparatus, thereby ensuring that the test mode is not accidentally initiated by an end user in the field.
In one version of this inventive IC module, the switching apparatus and the impedance apparatus are both incorporated in the die, and in other versions one or both of the switching apparatus and impedance apparatus are incorporated in a substrate of the IC module. In another version, the IC module itself is incorporated into an electronic system, such as a computer system. In still other versions, the operational mode signal is provided by an operational mode signal circuit on the die, or is provided by external circuitry through another terminal in the IC module. Finally, in a modified version of this inventive IC module, the test mode initiate signal is generated on the die by a test mode initiate signal circuit responsive to external circuitry rather than being provided by external circuitry.
In another embodiment of this invention, an IC module includes one or more terminals receiving a test mode initiate signal and an operational mode signal. One or more IC dice in the IC module each have one or more function circuits and a plurality of bond pads, and a first subset of the bond pads is coupled to the function circuits while a second subset of the bond pads is adapted to receive signals other than the test mode initiate signal in the test mode. A dedicated conduction circuit coupled between the terminals and the first subset bond pads and isolated from the second subset bond pads conducts the test mode initiate and operational mode signals to the function circuits. When the function circuits receive the test mode initiate signal, they initiate a test mode, and when the function circuits receive the operational mode signal, they enter an operational mode. Thus, a test mode can be initiated in the dice after they are packaged in the IC module by providing the test mode initiate signal at the terminals, and an operational mode can be initiated by providing the operational mode signal at the terminals. In one version of this IC module, the IC module is incorporated into an electronic system. In other versions, the terminals comprise a first terminal receiving the test mode initiate signal and a second terminal receiving the operational mode signal, and the first and second terminals are coupled by an impedance element, such as a resistor, or by a link, such as a surface mount resistor or a jumper.
In a further embodiment of this invention, a method for initiating a test mode and an operational mode in dice in an IC module includes: receiving a test mode initiate signal at a terminal of the IC module; conducting the test mode initiate signal only to those bond pads on dice in the IC module adapted to receive the signal and from those bond pads to function circuits in the dice to initiate a test mode therein; discontinuing conduction of the test mode initiate signal to the function circuits; and conducting an operational mode initiate signal to each function circuit to initiate the operational mode therein.
In a still further embodiment, a method for testing one or more dice in an IC module includes: providing a test mode initiate signal to an externally accessible terminal of the IC module; conducting the test mode initiate signal exclusively to bond pads on the dice adapted to receive the signal to initiate a test mode in the dice; testing each die; receiving response signals from the dice; and evaluating the response signals to identify any failing elements in the dice.